The present invention relates to a method of producing a semiconductor device. In particular, the present invention relates to a method of forming a wiring portion containing a high melting temperature metal.
When a wiring portion is formed of a high melting temperature metal, as compared with a wiring portion containing an aluminum alloy, it is possible to prevent a life of the wiring portion from being shortened due to electro-migration and reduce a cost thereof. Accordingly, it is preferred to use a wiring portion formed of a high melting temperature metal in a semiconductor device.
A conventional method of producing a semiconductor device will be explained with reference to FIGS. 11(A)-11(C) to 13(A)-13(B) (refer to Patent Reference).
Patent Reference Japanese Patent Publication No. 06-275625
FIGS. 11(A) to 11(C) are schematic sectional views showing the conventional method of producing the semiconductor device. FIGS. 12(A) to 12(C) are schematic sectional views showing the conventional method of producing the semiconductor device. FIGS. 13(A) and 13(B) are schematic sectional views showing the conventional method of producing the semiconductor device.
First, a base member 100 is prepared. The base member 100 is formed of a semiconductor substrate having an element such as a transistor formed thereon and an interlayer insulation film formed on the semiconductor substrate. A conductive plug is formed in the interlayer insulation film for electrically connecting the element formed in the semiconductor substrate to a wiring portion formed in a later step.
In the next step, a titanium nitride film is formed on the base member 100 with a sputter method. The titanium nitride film is referred to as a barrier film 120. Then, tungsten is deposited on the barrier film 120 with a CVD method to form a wiring portion film 130. Afterward, as shown in FIG. 11(A), a silicon nitride film 145 is formed on the wiring portion film 130 with a CVD method.
In the next step, as shown in FIG. 11(B), a resist is coated on the silicon nitride film 145 to form a resist film. The resist film is patterned through photolithography to form resist masks 160. The resist masks 160 cover wiring portion forming areas 105 such that wiring portion non-forming areas 107 are exposed.
In the next step, as shown in FIG. 11(C), the silicon nitride film 145 and the wiring portion film 130 are patterned using the resist masks 160 through RIE (Reactive Ion Etching). A SF6 gas is used as an etching gas.
An etching ratio of tungsten with respect to the resist is about 2.0. Accordingly, when the wiring portion film 130 is formed of a tungsten film, the resist masks 160 are etched in a vertical direction upon etching tungsten. As described later, the resist masks 160 have poor plasma resistance, so that the resist masks 160 are etched in a horizontal direction as well. In FIG. 11(C), there are shown etching remaining portions 162 of the resist masks 160 and etching remaining portions 147 of the silicon nitride film 145.
Further, when the SF6 gas is used as an etching gas, tungsten has a large etching ratio with respect to titanium nitride. Accordingly, as shown in FIG. 12(A), when the wiring portion film 130 is etched, the wiring portion film 130 in the wiring portion non-forming areas 107 is removed, and the wiring portion film 130 stops being etched when the barrier film 120 is exposed. That is, the barrier film 120 functions as an etching stopper.
Remaining portions of the wiring portion film 130 after the RIE are referred to as tungsten wiring portions 136 or wiring portions 136. Further, in FIG. 12(A), there are shown etching remaining portions 164 of the resist mask 160 and etching remaining portions 148 of the silicon nitride film 145.
In the next step, the RIE is performed using a Cl2 gas as an etching gas, so that portions of the barrier film 120 in the wiring portion non-forming areas 107 are removed, and etching remaining portions 122 of the barrier film 120 remain in the wiring portion forming areas 105. In the RIE using the Cl2 gas as an etching gas, tungsten has a large etching ratio with respect to titanium nitride. Accordingly, as shown in FIG. 12(B), when the barrier film 120 is etched, the tungsten wiring portions 136 are not etched to a large extent.
In the next step, as shown in FIG. 12(C), an NSG (Non-doped Silicate Glass) is deposited on the base member 100 with a CVD method to form an interlayer insulation film 170 embedding the wiring portions 136.
In the next step, as shown in FIG. 13(A), through holes 171 are formed in the interlayer insulation film 170 on the wiring portions 136 through photolithography and dry etching.
In the next step, as shown in FIG. 13(B), a titanium nitride film 182 and a metal film 184 are sequentially formed with a CVD method and a puttering method, so that the through holes 171 are filled with the titanium nitride film 182 and the metal film 184. The titanium nitride film 182 and the metal film 184 filling the through holes 171 are referred to as an upper layer metal wiring portion 180. The upper layer metal wiring portion 180 is electrically connected to the tungsten wiring portions 136 or lower layer wiring portions.
In the conventional method of producing the semiconductor device described above, the tungsten wiring portions 136 or lower layer wiring portions have a section with a forward tapered shape, in which a width of a bottom portion 136a on a base member side (lower side) becomes larger than a width of a top portion 136b on a resist mask side (upper side). The forward tapered shape is formed for the following reason.
When a fine wiring portion such as the wiring portions 136 having a width less than 150 nm is formed, a KrF excimer laser or an ArF excimer laser is used as a stepper. A KrF type resist or an ArF type resist used in this process has poor plasma resistance. Accordingly, during the RIE, a resist mask is etched not only in a vertical direction (an arrow direction G in FIG. 11(C)) but also a horizontal direction (an arrow direction H in FIG. 11(C)).
Accordingly, when the wiring film 136 formed of tungsten is etched, a width of the resist mask 160 decreases in the horizontal direction. When the wiring film 136 formed of tungsten is further etched, the width of the resist mask 160 gradually decreases. As a result, as shown in FIG. 12(B), the tungsten wiring portions 136 have the section with the forward tapered shape, in which a side surface 138 of the tungsten wiring portion 136 is inclined by an angle β of 80 degrees with respect to an upper surface 102 of the base member 100.
When the tungsten wiring portions 136 have the section with the forward tapered shape, a sectional area of the tungsten wiring portions 136 decreases by an amount proportional to the decrease in the width of the top portions 136b of the tungsten wiring portions 136 on the resist mask side. Due to the decrease in the sectional area, a wiring resistance of the tungsten wiring portions 136 increases, thereby deteriorating a performance of the semiconductor device.
Further, when the tungsten wiring portions 136 have the section with the forward tapered shape, the etching proceeds along the side surfaces 138 of the tungsten wiring portions 136 upon forming the through holes 171. As a result, a space X is formed next to the side surfaces 138 of the tungsten wiring portions 136 as shown in FIG. 13(A). When the titanium nitride film 182 is formed, the space X may not be filled with the titanium nitride film 182, thereby remaining as a space Y as shown in FIG. 13(B). Accordingly, a gas or chemical remaining in the space Y may deteriorate the tungsten wiring portions 136.
Further, when the tungsten wiring portions 136 have the section with the forward tapered shape, a contact area of the tungsten wiring portions 136 with respect to the titanium nitride film 18 thereabove decreases. As a result, a resistivity of the tungsten wiring portions 136 in the through holes 171 increases, thereby deteriorating a performance of the semiconductor device.
In view of the problems described above, an object of the present invention is to provide and a method of producing a semiconductor device capable of solving the problems of the conventional method of producing the semiconductor device. In the method of producing a semiconductor device, it is possible to obtain a tungsten wiring portion with a preferable sectional shape. Accordingly, it is possible to prevent a resistance of the tungsten wiring portion from increasing, and to prevent reliability of the wiring portion from decreasing.
Further objects and advantages of the invention will be apparent from the following description of the invention.